Machacek et al.
Milk modulates the gastrointestinal stability of tick-borne encephalitis virus: Implications for alimentary transmission J. Med. Virol. 2025, 98: e70778, doi.org/10.1002/jmv.70778
While the primary route of infection by the TBE virus is a tick bite, an alternative transmission route is the alimentary infection by non-pasteurized milk products. By consumption of non-pasteurized milk products, outbreaks are possible and have repeatedly been described (see e.g., Newsletter October 2022, Newsletter May 2022). Various thermal inactivation procedures of milk from cow, shee,p and goat have been shown to be effective (see e.g. Snapshot week 22/2025). A study has been carried out to analyze in detail the stability of the virus in milk, and its behavior in simulated gastric and intestinal conditions as well as how milk fractions can protect the virus against bile salts in the intestine.
When the TBE virus is stored in milk or PBS, a moderate but significant reduction in viral titer can be observed in both media at 8°C within a day and at 37°C after two hours. The destabilizing effect was stronger in various milk types compared to PBS. However, a considerable portion of viral particles remained infectious even after prolonged refrigeration.
A rapid inactivation (even after 1 min) of the virus was detected at acidic conditions (pH 1.5), while a higher tolerance was observed at pH 3. A further reduction of stability was observed when milk was added to TBE virus in low pH environments mimicking gastric conditions (pH 3, 4.5, and 6), indicating that milk components (probably free fatty acids like oleic acid) contribute to viral destabilization under acidic conditions. Fat fraction had a destabilizing effect at pH 3, but not at pH 4.5 or 6. Hydrolyzed casein and whey proteins showed destabilizing effects in an acidic environment.
Investigations under simulated intestinal conditions showed that bile salts mimicking the fed-state intestine led to rapid viral inactivation. When PBS was replaced with milk in the bile solution, a strong protective effect was observed at lower bile concentration. While the fat fraction failed to protect the virus, skim milk fraction conferred partial protection. Intact casein showed the best protection in counteracting bile salt disruption. Casein can bind bile salts, offering a plausible mechanism for the observed protection.
To sum up, milk can contribute to viral destabilization in an acidic environment in the stomach, but can protect the virus in the intestine – likely through casein-mediated sequestration of bile salts.